The present invention relates to television compositing systems, and more particularly to a simple compositing system for combining many image sequences into a final composite image sequence using a minimum of hardware.
Television post-production involves the combination of many image sequences into a final composite image sequence. These image sequences typically represent the projection of a three-dimensional (3D) object onto a monitor screen. Generally these objects do not fill an entire television raster scan active picture area, and are sometimes translucent. Also these objects are usually in motion. 3D graphics rendering computers are a common source of artificial image sequences. Generation of the graphics image sequence is usually slow (less than ten frames per second to minutes or hours per frame depending upon the complexity of the objects in the image sequence). A digital picture manipulator (DPM), such as the Kaleidoscope DPM manufactured by The Grass Valley Group, Inc. of Grass Valley, California, United States of America, can transform a two-dimensional (2D) image into a 3D projection on the monitor screen. The input to and output from the DPM is typically video having moving objects. While the DPM output is similar to a rendering computer, the DPM's role is one of processing video from some other source rather than generating the video. Also the DPM processes video in real time (25 or 30 frames per second).
The output of a rendering computer is often combined with other video from other sources, such as video recorders, cameras and the like. Likewise the outputs of several DPM channels are combined. Combination of a rendered graphics image with one or more images processed via DPMs is common as well. The most common mechanism for integrating rendered images with realtime video source material is to record the graphics image on a disk-based recorder one frame at a time. The disk recorder is then capable of realtime playback. The rendering computer is usually not considered to be part of a realtime compositing system. Rather it does its job off line and stores its result on the disk recorder or a pair of video tape recorders (one for video and the other for key). That temporary storage is then moved (logically or physically) into the compositing room.
A typical DPM has several processing channels and a combiner which composites the outputs of the DPM channels. Some DPMs, such as the Kaleidoscope DPM, have an extra input to the combiner that allows the video and key from an external device to be merged with the DPM channel outputs. This input is not processed by the DPM and may include graphics image sequences. In this configuration the combiner's output typically is a full screen image and no key signal is required. However, the combiner's output may not be full screen, in which case a key signal also is recorded on a second recording device. The primary drawback of this type of compositing system is its cost, but the system does composite images in real time. The cost is in the playback and recording devices as well as the DPM channels, each of which cost in excess of $100,000.00.
What is desired is a simple compositing system that combines images from several sources, including graphics images and video images, in an inexpensive manner.